Magnetic recording device and magnetic recording apparatus

ABSTRACT

An example magnetic recording device includes a laminated body. The laminated body includes a first ferromagnetic layer with a magnetization substantially fixed in a first direction; a second ferromagnetic layer with a variable magnetization direction; a first nonmagnetic layer disposed between the first ferromagnetic layer and the second ferromagnetic layer; a third ferromagnetic layer with a variable magnetization direction; and a fourth ferromagnetic layer with a magnetization substantially fixed in a second direction, wherein at least one of the first and second direction is generally perpendicular to the film plane. The magnetization direction of the second ferromagnetic layer is determinable in response to the orientation of a current, by passing the current in a direction generally perpendicular to the film plane of the layers of the laminated body and the magnetization of the third ferromagnetic layer is able to undergo precession by passing the current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2007-182286, filed on Jul. 11,2007; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a magnetic recording device and a magneticrecording apparatus in which a radio-frequency magnetic field is appliedin combination with a write current.

2. Background Art

Applying a magnetic field is a conventional method for controlling themagnetization direction of a magnetic material. For example, in a harddisk drive (HDD), the magnetization direction of a medium is reversed bya magnetic field generated from a recording head to perform writeoperation. In a conventional magnetic random access memory, a current ispassed through an interconnect disposed near a magnetoresistive effectdevice to generate a current-induced magnetic field, which is applied toa cell to control the magnetization direction of the cell. These methodsfor controlling the magnetization direction by an external magneticfield (writing methods based on a current-induced magnetic field) have along history and can be regarded as well-established techniques.

On the other hand, the recent progress in nanotechnology has enabledsignificant downscaling of magnetic materials. This has created a needto locally control magnetization at the nanoscale. However, a magneticfield intrinsically has the nature of spreading in space, and isdifficult to localize. In selecting a particular bit or cell andcontrolling its magnetization direction, the problem of “crosstalk”,that is, extension of magnetic field to an adjacent bit or cell, becomesprominent with the downscaling of the bit or cell. On the contrary,downsizing the source of magnetic field to localize the magnetic fieldcauses the problem of failing to generate a magnetic field enough tocontrol the magnetization direction.

As a technique for solving these problems, the “spin injection inducedmagnetization reversal” is proposed, in which a current is passedthrough a magnetic material to induce magnetization reversal (e.g., F.J. Albert, et al., Appl. Phys. Lett. 77, 3809 (2000), hereinafterreferred to as Non-Patent Document 1).

In the technique disclosed in Non-Patent Document 1, a spin injectioncurrent serving as a write current is passed through a magnetoresistiveeffect device to generate spin-polarized electrons, which are used formagnetization reversal. Specifically, the angular momentum ofspin-polarized electrons is transferred to electrons in a magneticmaterial serving as a magnetic recording layer, and thereby themagnetization of the magnetic recording layer is reversed.

This type of technique for magnetization reversal directly driven bycurrent (spin injection induced magnetization reversal technique)facilitates locally controlling magnetization at the nanoscale, and thevalue of the spin injection current can be decreased in accordance withthe downscaling of the magnetic material. This facilitates realizingspin electronics devices such as hard disk drives and magnetic randomaccess memories with high recording density.

Furthermore, there is a magnetic recording apparatus in which analternating current is passed through a bit line or a word line togenerate an alternating magnetic field (e.g., United States PatentApplication Publication No. 2007/0047294, hereinafter referred to asPatent Document 1).

The magnetic recording apparatus disclosed in Patent Document 1comprises a matrix of recording cells, each being addressable by a row(bit line) and a column (word line). Each magnetic cell has aferromagnetic pinned layer, a barrier layer, and a ferromagnetic freelayer (recording layer), and is subjected to writing in accordance withthe orientation of current. Each magnetic cell is provided with aseries-connected switching device (transistor). Each magnetic cell isconnected to one bit line, and each switching device (transistor) isconnected to one word line. The apparatus further includes a directcurrent power supply for passing a direct current at the time ofrecording, and an alternating current power supply for generating analternating magnetic field.

-   Non-Patent Document 2: Shehzaad Kaka, et al., Journal of Magnetism    and Magnetic Materials, Volume 286 (2005) p. 375

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a magneticrecording device including: a laminated body including: a firstferromagnetic layer with a magnetization substantially fixed in a firstdirection; a second ferromagnetic layer with a variable magnetizationdirection; a first nonmagnetic layer disposed between the firstferromagnetic layer and the second ferromagnetic layer; and a thirdferromagnetic layer with a variable magnetization direction, themagnetization direction of the second ferromagnetic layer beingdeterminable in response to the orientation of a current, by allowingelectrons spin-polarized by passing a current in a direction generallyperpendicular to the film plane of the layers of the laminated body toact on the second ferromagnetic layer, and by allowing a magnetic fieldgenerated by precession of the magnetization of the third ferromagneticlayer to act on the second ferromagnetic layer.

According to an aspect of the invention, there is provided a magneticrecording device including: a laminated body including a firstferromagnetic layer with a magnetization substantially fixed in a firstdirection, a second ferromagnetic layer with a variable magnetizationdirection, and a first nonmagnetic layer disposed between the firstferromagnetic layer and the second ferromagnetic layer; and a thirdferromagnetic layer with a variable magnetization direction disposedclose to the second ferromagnetic layer, the magnetization direction ofthe second ferromagnetic layer being determinable in response to theorientation of a current, by allowing electrons spin-polarized bypassing a current in a direction generally perpendicular to the filmplane of the layers of the laminated body to act on the secondferromagnetic layer, and by allowing a magnetic field generated byprecession of the magnetization of the third ferromagnetic layer to acton the second ferromagnetic layer.

According to an aspect of the invention, there is provided a magneticrecording apparatus including: a plurality of memory cells arranged in amatrix, each memory cell including the magnetic recording deviceincluding: a laminated body including: a first ferromagnetic layer witha magnetization substantially fixed in a first direction; a secondferromagnetic layer with a variable magnetization direction; a firstnonmagnetic layer disposed between the first ferromagnetic layer and thesecond ferromagnetic layer; and a third ferromagnetic layer with avariable magnetization direction, the magnetization direction of thesecond ferromagnetic layer being determinable in response to theorientation of a current, by allowing electrons spin-polarized bypassing a current in a direction generally perpendicular to the filmplane of the layers of the laminated body to act on the secondferromagnetic layer, and by allowing a magnetic field generated byprecession of the magnetization of the third ferromagnetic layer to acton the second ferromagnetic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a basic cross-sectionalstructure of a magnetic recording device according to a first embodimentof the invention;

FIGS. 2A and 2B are schematic cross-sectional views for illustrating themechanism of “writing” in the magnetic recording device shown in FIG. 1;

FIGS. 3A and 3B are schematic cross-sectional views for illustrating themechanism of “reading” in the magnetic recording device shown in FIG. 1;

FIGS. 4A to 4E are schematic views illustrating the intermediate layerdisposed between the magnetic recording layer and the magnetizationrotation layer according to this embodiment;

FIG. 5 is a schematic view illustrating the cross-sectional structure ofa magnetic recording device according to a specific example of thisembodiment;

FIG. 6 is a schematic view illustrating the cross-sectional structure ofa magnetic recording device according to another specific example ofthis embodiment;

FIG. 7 is a schematic view illustrating the cross-sectional structure ofa magnetic recording device according to still another specific exampleof this embodiment;

FIG. 8 is a graph illustrating the temporal variation of magnetizationreversal;

FIG. 9 is a graph illustrating the temporal variation of magnetizationreversal;

FIGS. 10A to 10E are graphs illustrating the temporal variation ofmagnetic reversal;

FIG. 11 is a schematic illustration of the dependence of time requiredfor magnetization reversal on frequency and radio-frequency magneticfield intensity;

FIG. 12 is a table showing the result of writing probability in thisworking example;

FIG. 13 is a schematic view illustrating a basic cross-sectionalstructure of a magnetic recording device according to a secondembodiment of the invention;

FIG. 14 is a schematic view illustrating another basic cross-sectionalstructure of a magnetic recording device according to the secondembodiment of the invention;

FIG. 15 is a schematic view illustrating the cross-sectional structureof a magnetic recording device according to a specific example of thisembodiment;

FIG. 16 is a schematic view illustrating the cross-sectional structureof a magnetic recording device according to another specific example ofthis embodiment;

FIG. 17 is a schematic view illustrating the cross-sectional structureof a magnetic recording device according to another specific example ofthis embodiment;

FIG. 18 is a schematic view illustrating the cross-sectional structureof a magnetic recording device according to still another specificexample of this embodiment; and

FIG. 19 is a plan view illustrating a magnetic recording apparatusaccording to a third embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will now be described with reference to thedrawings, where similar components are labeled with like referencenumerals, and the detailed description thereof is omitted asappropriate.

FIG. 1 is a schematic view illustrating a basic cross-sectionalstructure of a magnetic recording device according to a first embodimentof the invention.

This magnetic recording device comprises a magnetic recording section 3and a magnetization oscillator 5. The magnetic recording section 3 andthe magnetization oscillator 5 are disposed adjacently across anintermediate layer 40 a.

The magnetic recording section 3 includes a magnetic pinned layer 10 awith a magnetization 12 a fixed generally parallel to the film plane, amagnetic recording layer 30 with a magnetization easy axis 34 directedgenerally parallel to the film plane, and a nonmagnetic barrier layer 20disposed between the magnetic pinned layer 10 a and the magneticrecording layer 30. This laminated structure composed of the magneticpinned layer 10 a, the barrier layer 20, and the magnetic recordinglayer 30 is known as MTJ (magnetic tunnel junction).

The magnetization oscillator 5 includes a magnetization rotation layer50 including a magnetic layer with a magnetization easy axis 54 directedgenerally parallel to the film plane, a magnetic pinned layer 10 b witha magnetization 12 b fixed generally perpendicular to the film plane,and an intermediate layer 40 b disposed between the magnetizationrotation layer 50 and the magnetic pinned layer 10 b.

In the magnetic pinned layer 10 b, alternatively, the magnetization 12 bcan be fixed generally parallel to the film plane. The magnetizationrotation layer 50 and the magnetic pinned layer 10 b are different inmaterial. For example, the magnetization rotation layer 50 can be madeof permalloy (Py), the intermediate layer 40 b can be made of copper(Cu), and the magnetic pinned layer 10 b can be made of cobalt (Co).Permalloy (Py) is a NiFe-based alloy. The direction of the magnetizationeasy axis 54 of the magnetization rotation layer 50 may be orthogonal tothe direction of the magnetization easy axis 34 of the magneticrecording layer 30. The intermediate layer 40 a disposed between themagnetic recording section 3 and the magnetization oscillator 5 is, soto speak, a spin quenching layer, having a nonmagnetic material orstructure in which the spin polarization of electrons flowing generallyperpendicular to the film plane of the intermediate layer 40 a isquenched by the intermediate layer 40 a.

The magnetic recording device of this embodiment has a structure inwhich the magnetic pinned layer 10 b, the intermediate layer 40 b, themagnetization rotation layer 50, the intermediate layer 40 a, themagnetic recording layer 30, the barrier layer 20, and the magneticpinned layer 10 a are laminated in this order. An electron current 60can be passed through this magnetic recording device using electrodes,not shown, connected to the magnetic pinned layers 10 a, 10 b. Themagnetic recording layer 30 serves for recording, and its magnetizationcan be reversed relatively easily in the direction of the magnetizationeasy axis 34. The magnetization rotation layer 50 serves to generate aradio-frequency magnetic field at the time of recording.

The magnetic pinned layers 10 a, 10 b, the magnetic recording layer 30,and the magnetization rotation layer 50 are made of magnetic materials.The magnetization pinning of the magnetic pinned layer 10 a, 10 b can bereinforced by disposing an antiferromagnetic layer, not shown, adjacentto the magnetic pinned layer 10 a, 10 b. Each of the magnetic pinnedlayers 10 a, 10 b, the magnetic recording layer 30, and themagnetization rotation layer 50 can be a single layer, or can be made ofmultilayer films, which are ferromagnetically or antiferromagneticallycoupled to each other. The barrier layer is made of a nonmagnetic,high-resistance insulating material or semiconductor. The intermediatelayer 40 a, 40 b is made of a nonmagnetic conductive metal,semiconductor, or insulator.

In the magnetic recording device of this embodiment, the magneticrecording layer 30 made of a magnetic material is adjacent to themagnetization rotation layer 50. Hence a material having spin quenchingcapability is used for the intermediate layer 40 a. If spin informationis retained in the intermediate layer 40 a as in the conventional case,spin transfer torque from the magnetic recording layer 30 affects themagnetization rotation layer 50 and decreases the controllability of themagnetization rotation of the magnetization rotation layer 50. Thus therotation direction may be varied with the orientation of current flow.To prevent this, the intermediate layer 40 a is provided with spinquenching capability. Furthermore, the thickness of the intermediatelayer 40 a is preferably 1.4 nm or more so as to avoid interlayermagnetic coupling between the magnetic recording layer 30 and themagnetization rotation layer 50.

In the magnetic recording device according to this embodiment, themagnetization direction of the magnetic recording layer 30 can becontrolled by passing an electron current 60 between the upper and lowermagnetic pinned layer 10 a, 10 b. Specifically, the magnetizationorientation of the magnetic recording layer 30 can be reversed byswitching the flowing orientation (polarity) of the electron current 60.Information can be recorded by assigning “0” and “1” to eachmagnetization direction of the magnetic recording layer 30.

Here, the basic mechanism of “writing” in the magnetic recording deviceis described.

FIG. 2 is a schematic cross-sectional view for illustrating themechanism of “writing” in the magnetic recording device shown in FIG. 1.More specifically, FIG. 2A is a schematic cross-sectional view showingthe case where an electron current 60 is passed from the magnetic pinnedlayer 10 a toward the magnetic recording layer 30, and FIG. 2B is aschematic cross-sectional view showing the case where an electroncurrent 60 is passed from the magnetic recording layer 30 toward themagnetic pinned layer 10 a. For convenience, the magnetizationoscillator 5 and the intermediate layer 40 a in the magnetic recordingdevice shown in FIG. 1 are omitted.

The mechanism of writing to the magnetic recording layer 30 by passingan electron current 60 across the film plane of the magnetic pinnedlayer 10 a and the magnetic recording layer 30 is described as follows.The description is given of the case where the magnetoresistive effectthrough the barrier layer 20 is of the normal type. Here, themagnetoresistive effect of the “normal type” refers to the case wherethe electric resistance is higher when the magnetizations of themagnetic layers on both sides of the barrier layer are antiparallel thanwhen they are parallel. That is, in the case of the normal type, theelectric resistance between the magnetic pinned layer 10 a and themagnetic recording layer 30 through the barrier layer 20 is lower whenthe magnetizations of the magnetic pinned layer 10 a and the magneticrecording layer 30 are parallel than when they are antiparallel.

First, in FIG. 2A, electrons that have passed through the magneticpinned layer 10 a having a magnetization 12 a generally parallel to thefilm plane take on spin parallel to the magnetization 12 a. When theseelectrons flow into the magnetic recording layer 30, the angularmomentum of this spin is transferred to the magnetic recording layer 30and acts on its magnetization 32, that is, a so-called spin transfertorque is exerted thereon. Thus the magnetic recording layer 30 takes ona magnetization 32 parallel (rightward in this figure) to themagnetization 12 a. To the magnetic recording layer 30 having themagnetization 32 of this orientation (rightward in this figure), “0” isillustratively assigned.

FIG. 2B shows the case where the orientation of the electron current 60is reversed. Among the electrons that have passed through the barrierlayer 20, electrons with spin parallel (rightward in this figure) to themagnetization 12 a pass through the magnetic pinned layer 10 a, whereaselectrons with spin antiparallel (leftward in this figure) to themagnetization 12 a are reflected at the interface between the magneticpinned layer 10 a and the barrier layer 20. The angular momentum of thespin of these reflected electrons is transferred to the magneticrecording layer 30 and acts on its magnetization 32, that is, aso-called spin transfer torque is exerted thereon. Thus the magneticrecording layer 30 takes on a magnetization 32 antiparallel (leftward inthis figure) to the magnetization 12 a. To the magnetic recording layer30 having the magnetization 32 of this orientation (leftward in thisfigure), “1” is illustratively assigned.

By the foregoing action, “0” and “1” are suitably assigned to themagnetic recording layer 30, and “writing” in the magnetic recordingdevice is completed. The foregoing has described the case where themagnetoresistive effect between the magnetic pinned layer 10 a and themagnetic recording layer 30 through the barrier layer 20 is of the“normal type”.

The magnetoresistive effect of the “reverse type” refers to the casewhere the electric resistance is higher when the magnetizations of themagnetic layers on both sides of the barrier layer are parallel thanwhen they are antiparallel. That is, in the case of the reverse type,the electric resistance between the magnetic pinned layer 10 a and themagnetic recording layer 30 through the barrier layer 20 is higher whenthe magnetizations of the magnetic pinned layer 10 a and the magneticrecording layer 30 are parallel than when they are antiparallel. Thus,electrons that have passed through the magnetic pinned layer 10 a takeon spin antiparallel to the magnetization 12 a. Furthermore, electronswith spin parallel to the magnetization 12 a are reflected, whereaselectrons with spin antiparallel to the magnetization 12 a pass throughthe magnetic pinned layer 10 a. The subsequent mechanism of “writing” isthe same as that for the case where the magnetoresistive effect is ofthe “normal type”, and hence the detailed description thereof isomitted.

Next, the mechanism of “reading” in the magnetic recording device isdescribed.

In the magnetic recording device of this embodiment, the direction ofthe magnetization 32 of the magnetic recording layer 30 can be detectedby using the “magnetoresistive effect” in which the electric resistancevaries with the relative orientation of the magnetization of each layer.That is, in the case of using the magnetoresistive effect, themagnetoresistance can be measured by passing a sense current 61 betweenthe magnetic pinned layer 10 a and the magnetic recording layer 30. Thevalue of the sense current 61 is lower than the value of the electroncurrent 60 passed at the time of recording.

FIG. 3 is a schematic cross-sectional view for illustrating themechanism of “reading” in the magnetic recording device shown in FIG. 1.More specifically, FIG. 3A is a schematic cross-sectional view showingthe case where the magnetization 12 a of the magnetic pinned layer 10 ais parallel to the magnetization 32 of the magnetic recording layer 30,and FIG. 3B is a schematic cross-sectional view showing the case wherethe magnetization 12 a of the magnetic pinned layer 10 a is antiparallelto the magnetization 32 of the magnetic recording layer 30. Forconvenience, the magnetization oscillator 5 and the intermediate layer40 a in the magnetic recording device shown in FIG. 1 are omitted.

In the magnetic recording device shown in FIG. 3A, the magnetoresistancedetected by passing a sense current 61 has a relatively low value in themagnetoresistive effect of the normal type, and a relatively high valuein the magnetoresistive effect of the reverse type.

In the magnetic recording device shown in FIG. 3B, the magnetoresistancedetected by passing a sense current 61 has a relatively high value inthe magnetoresistive effect of the normal type, and a relatively lowvalue in the magnetoresistive effect of the reverse type.

Recording and reading of a binary data can be made by associating “0”and “1” with these states with different resistances. Alternatively, theorientation of the sense current 61 can be opposite (upward in FIG. 3)to the direction of the arrow shown in FIG. 3.

Next, the operation of the magnetic recording device according to thisembodiment at the time of recording is described.

In the magnetic recording device of this embodiment, in the case wherean electron current 60 flows from the magnetic pinned layer 10 a to themagnetic recording layer 30 in FIG. 1 (downward in this figure),electrons passing through the magnetic pinned layer 10 a take on spinparallel to the magnetization 12 a as described above. Hence themagnetic recording layer 30 takes on a magnetization 32 parallel(leftward in this figure) to the magnetization 12 a.

Simultaneously with this write operation, the electron current 60 flowsfrom the magnetization rotation layer 50 to the magnetic pinned layer 10b (downward in this figure). Hence, electrons with spin parallel to themagnetization 12 b of the magnetic pinned layer 10 b pass through themagnetic pinned layer 10 b, whereas electrons with spin antiparallel tothe magnetization 12 b are reflected at the interface between themagnetic pinned layer 10 b and the intermediate layer 40 b. When thesereflected electrons flow into the magnetization rotation layer 50, themagnetization of the magnetization rotation layer 50 undergoesprecession by the effect of the electron spin (spin transfer torque).Consequently, a radio-frequency magnetic field is generated from themagnetization rotation layer 50.

On the other hand, the electron current 60 that has passed through themagnetic recording layer 30 of the magnetic recording section 3 alsoacts on the magnetization of the magnetization rotation layer 50 of themagnetization oscillator 5. However, the intermediate layer 40 a made ofa spin quenching layer is interposed between the magnetic recordinglayer 30 and the magnetization rotation layer 50, and hence the spininformation of electrons traversing the intermediate layer 40 a issignificantly attenuated. Consequently, the magnetization of themagnetization rotation layer 50 can be controlled independently of theeffect of the electron spin (spin transfer torque) from the magneticrecording layer 30.

In contrast, in the case—where an electron current 60 flows from themagnetic recording layer 30 to the magnetic pinned layer 10 a in FIG. 1(upward in this figure), electrons with spin parallel to themagnetization 12 a of the magnetic pinned layer 10 a pass through themagnetic pinned layer 10 a, whereas electrons with spin antiparallel tothe magnetization 12 a are reflected at the interface between themagnetic pinned layer 10 a and the barrier layer 20. When thesereflected electrons flow into the magnetic recording layer 30, themagnetic recording layer 30 takes on a magnetization 32 antiparallel(rightward in this figure) to the magnetization 12 a by the effect ofthe electron spin.

Simultaneously with this write operation, the electron current 60 flowsfrom the magnetic pinned layer 10 b to the magnetization rotation layer50 (upward in this figure). Electrons passing through the magneticpinned layer 10 b take on spin parallel to the magnetization 12 b. Whenthese electrons flow into the magnetization rotation layer 50, themagnetization of the magnetization rotation layer 50 undergoesprecession by the effect of the electron spin (spin transfer torque).Consequently, a radio-frequency magnetic field is generated from themagnetization rotation layer 50.

On the other hand, part of the electron current 60 that has flowed fromthe magnetization rotation layer 50 of the magnetization oscillator 5 tothe magnetic recording layer 30 of the magnetic recording section 3 isreflected at the surface of the magnetic recording layer 30 and alsoacts on the magnetization of the magnetization rotation layer 50 of themagnetization oscillator 5. However, the intermediate layer 40 a made ofa spin quenching layer is interposed between the magnetic recordinglayer 30 and the magnetization rotation layer 50, and hence the spininformation of electrons traversing the intermediate layer 40 a issignificantly attenuated. Consequently, the magnetization of themagnetization rotation layer 50 can be controlled independently of theeffect of the electron spin (spin transfer torque) from the magneticrecording layer 30.

The frequency of the radio-frequency magnetic field is approximately 1to 60 GHz, for example. This radio-frequency magnetic field has acomponent perpendicular to the magnetization easy axis of the magneticrecording layer 30, that is, in the direction of its magnetization hardaxis. Hence, at least part of the radio-frequency magnetic fieldgenerated from the magnetization rotation layer 50 is applied in thedirection of the magnetization hard axis of the magnetic recording layer30. When the radio-frequency magnetic field generated from themagnetization rotation layer 50 is applied in the direction of themagnetization hard axis of the magnetic recording layer 30, themagnetization 32 of the magnetic recording layer 30 becomes very easy tobe reversed.

If the magnetization 32 of the magnetic recording layer 30 is easy to bereversed, the magnetization reversal rate can be increased. Furthermore,the reversal variation of the magnetization 32 is reduced. Thus thevalue of write current can be decreased.

As described above, according to this embodiment, the magnetizationrotation layer 50 for generating a radio-frequency magnetic field isadjacent to the magnetic recording layer 30, the intermediate layer 40 amade of a spin quenching layer is interposed between the magnetizationrotation layer 50 and the magnetic recording layer 30, and the effect ofspin transfer torque is not exerted on each other. Hence themagnetization 32 has a good reversal efficiency and controllability.This allows increased reversal rate and reduced variation inmagnetization reversal without degrading thermal fluctuation resistanceand MR (magnetoresistive effect) characteristics. Furthermore, the valueof write current can be also reduced. If the intermediate layer 40 a ismade of a spin conduction layer as described later, a control of themagnetization of the magnetization rotation layer 50 becomes difficultand the magnetic recording layer 30 becomes less stable.

Next, elements constituting the magnetic recording device of thisembodiment are described in detail.

For the magnetic pinned layers 10 a, 10 b, one of a magnetic layer witha magnetization fixed generally parallel to the film plane and amagnetic layer with a magnetization fixed generally perpendicular to thefilm plane can be suitably selected in accordance with characteristicsrequirements. For the magnetic recording layer 30 and the magnetizationrotation layer 50, one of a magnetic layer with a magnetization easyaxis directed generally parallel to the film plane and a magnetic layerwith a magnetization easy axis directed generally perpendicular to thefilm plane can be suitably selected in accordance with characteristicsrequirements.

The magnetic pinned layer 10 a, 10 b, the magnetic recording layer 30,or the magnetization rotation layer 50 made of a magnetic layer with amagnetization easy axis directed generally perpendicular to the filmplane can be made of an alloy in which at least one element selectedfrom the group consisting of iron (Fe), cobalt (Co), nickel (Ni),manganese (Mn), and chromium (Cr) is combined with at least one elementselected from the group consisting of platinum (Pt), palladium (Pd),iridium (Ir), ruthenium (Ru), and rhodium (Rh). The characteristicsthereof can be adjusted by the composition and/or heat treatment ofconstituent magnetic materials. Alternatively, these layers can be madeof an amorphous alloy of rare earth and transition metal such as TbFeCoand GdFeCo, or a laminated structure of Co/Pt or Co/Pd.

As another example of magnetic films having a magnetization easy axisdirected generally perpendicular to the film plane, stacked structureshaving alloy films having showing a perpendicular magnetization based onordered alloys such as FePt, FeCoPt, FePd and CoPd, and a very thinlayer of CoFeB can be used. A single layer of CoFeB has a magnetizationeasy axis parallel to a film plane, however, the magnetization easy axisof the CoFeB becomes perpendicular to the film plane if it is stackedwith a perpendicular magnetization film.

The magnetic pinned layer 10 a, 10 b, the magnetic recording layer 30,or the magnetization rotation layer 50 made of a magnetic layer with amagnetization easy axis directed generally perpendicular to the filmplane is not limited to these continuous magnetic materials, but can bea composite structure in which fine particles made of a magneticmaterial are precipitated as a matrix in a nonmagnetic material, orcovered with a nonmagnetic material (fine magnetic material, describedlater). Such composite structures illustratively include the so-called“granular magnetic material” and “core shell structure”. The compositestructure containing fine particles is suitable for downscaling thedevice, and hence suitable for increasing the packaging density. Themagnetic fine particle has a cylindrical or spherical shape. With regardto the composite structure, in the case where the nonmagnetic materialis made of an oxide-based high-resistance material such as Al₂O_(3-x),MgO_(1-x), SiO_(x), ZnO_(x), and TiO_(x), the spin injection currentserving as a write current concentrates on fine particles, which allowsmagnetization reversal at a low current density. In particular, if thenonmagnetic material used is the same as the material of the nonmagneticbarrier layer 20, crystal control and magnetic anisotropy control offine particles are facilitated.

The magnetic pinned layer 10 a, 10 b, the magnetic recording layer 30,or the magnetization rotation layer 50 made of a magnetic layer with amagnetization easy axis directed generally parallel to the film plane isillustratively made of a magnetic metal containing at least one elementselected from the group consisting of iron (Fe), cobalt (Co), nickel(Ni), manganese (Mn), and chromium (Cr).

In the case where the above magnetic materials are used for magneticlayers, the frequency of the radio-frequency magnetic field generatedfrom the magnetization rotation layer 50 can be tuned by adjusting themagnetic anisotropy and saturation magnetization. However, the magneticanisotropy Ku of the magnetic recording layer 30 preferably satisfiesthe condition of KuV/kT>30 from the viewpoint of recording retention.

Alternatively, the magnetic layer of the magnetic pinned layer 10 a, 10b, the magnetic recording layer 30, or the magnetization rotation layer50 can be a laminated ferri layer. This is intended to increase theoscillation frequency of the magnetization rotation layer 50, orefficiently pin the magnetization of the magnetic pinned layer 10 a, 10b. Furthermore, a laminated structure of different magnetic layers canalso be used to improve characteristics. Moreover, it is also possibleto use a lamination in which a magnetic layer with a magnetization easyaxis directed generally parallel to the film plane is laminated with amagnetic layer with a magnetization easy axis directed generallyperpendicular to the film plane.

The thickness of the magnetic recording layer 30 or the magnetizationrotation layer 50 is preferably in the range of 1 to 15 nm (except thethickness of the nonmagnetic layer in the case of a laminated film).This is intended to induce the magnetization reversal of the magneticrecording layer 30 and the precession of the magnetization rotationlayer 50 without compromising device characteristics.

The barrier layer 20 can be made of an insulating material serving as atunnel barrier layer for producing a large reproduction signal output bythe TMR (tunneling magnetoresistive) effect at the time of reading.Specifically, the nonmagnetic barrier layer can be made of an oxide,nitride, or fluoride containing at least one element selected from thegroup consisting of aluminum (Al), titanium (Ti), zinc (Zn), zirconium(Zr), tantalum (Ta), cobalt (Co), nickel (Ni), silicon (Si), magnesium(Mg), and iron (Fe).

In particular, the nonmagnetic barrier layer is preferably made of aninsulator such as alumina (Al₂O_(3-x)), magnesium oxide (MgO),SiO_(2-x), Si—O—N, Ta—O, Al—Zr—O, ZnO_(x), and TiO_(x), or asemiconductor having a large energy gap (such as GaAlAs). Furthermore,the nonmagnetic barrier layer can be made of a nanocontact MR(magnetoresistive effect) material in which a magnetic material isinserted into pinholes provided in an insulator, or a CCP (confinedcurrent pass)-CPP (current perpendicular to plane)-MR material in whichcopper (Cu) is inserted into pinholes provided in an insulator, toproduce a large reproduction signal output.

In the case where the nonmagnetic barrier layer is a tunnel barrierlayer, its thickness is preferably in the range of e.g. approximately0.2 to 2.0 nm to produce a large reproduction signal output. Likewise,in the case where the nonmagnetic barrier layer is a nanocontact MRmaterial, its thickness is preferably in the range of e.g. approximately0.4 to 40 nm to produce a large reproduction signal output.

FIG. 4 is a schematic view illustrating the intermediate layer disposedbetween the magnetic recording layer and the magnetization rotationlayer according to this embodiment. More specifically, FIG. 4A is aschematic view illustrating an intermediate layer made of a single layerfilm. FIG. 4B is a schematic view illustrating an intermediate layermade of a laminated film in which a copper (Cu) layer is laminated onone side. FIG. 4C is a schematic view illustrating an intermediate layermade of a laminated film in which a copper (Cu) layer is laminated onboth sides. FIG. 4D is a schematic view illustrating an intermediatelayer made of a laminated film in which an oxide is laminated on oneside. FIG. 4E is a schematic view illustrating an intermediate layermade of a laminated film in which an oxide is laminated on both sides.

In the case where the magnetic recording layer 30 is adjacent to themagnetization rotation layer 50 across the intermediate layer 40 a likethe magnetic recording device shown in FIG. 1, the intermediate layer 40a is made of a layer (spin quenching layer) 80 including a nonmagneticmaterial or structure in which the spin polarization of electronspassing therethrough is attenuated. In studying spin injection inducedmagnetization reversal for magnetic recording devices having a layeredstructure including CoFe/Ru/CoFe, the inventors have found thatruthenium (Ru) has an extremely short effective spin diffusion length ofseveral nm, and found the effect of quenching the spin polarization ofelectrons passing through a ruthenium (Ru) layer.

This spin quenching effect is caused by quenching of spin inside theruthenium (Ru) layer and the spin-flip effect at the interface betweenthe ruthenium (Ru) layer and its adjacent layer. Materials of theintermediate layer 40 a that provide such a spin quenching effectinclude a metal selected from the group consisting of ruthenium (Ru),tantalum (Ta), tungsten (W), platinum (Pt), palladium (Pd), molybdenum(Mo), niobium (Nb), zirconium (Zr), titanium (Ti), and vanadium (V), oran alloy containing at least one element thereof.

The thickness of the intermediate layer 40 a is preferably 1.4 nm ormore and 20 nm or less. If it is 1.4 nm or more, no interlayer magneticcoupling occurs between the magnetic recording layer 30 and themagnetization rotation layer 50, and it is possible to quench the spinpolarization of conduction electrons passing through the inside andinterface of the intermediate layer 40 a. Furthermore, the precession ofthe magnetization rotation layer 50 can be prevented from varying withthe magnetization orientation of the magnetic recording layer 30. On theother hand, the thickness above 20 nm is undesirable because the pillarformation in the multilayer film is made difficult.

Besides the single layer film 80 described above, the intermediate layer40 a can be a laminated film in which a copper (Cu) layer 90 islaminated on one side or both sides of a layer made of a metal selectedfrom the group consisting of ruthenium (Ru), tantalum (Ta), tungsten(W), platinum (Pt), palladium (Pd), molybdenum (Mo), niobium (Nb),zirconium (Zr), titanium (Ti), and vanadium (V), or an alloy containingat least one element thereof.

Furthermore, besides the single layer film 80 described above, theintermediate layer 40 a can be a laminated film in which an oxide 100containing at least one element selected from the group consisting ofaluminum (Al), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co),nickel (Ni), vanadium (V), chromium-(Cr), tantalum (Ta), tungsten (W),and ruthenium (Ru) is laminated on one side or both sides of a layermade of a metal selected from the group consisting of ruthenium (Ru),tantalum (Ta), tungsten (W), platinum (Pt), palladium (Pd), molybdenum(Mo), niobium (Nb), zirconium (Zr), titanium (Ti), and vanadium (V), oran alloy containing at least one element thereof.

If the intermediate layer 40 a is made of a laminated film in which acopper (Cu) layer 90 is laminated, the motion of the magnetization ofthe magnetic recording layer 30 or the magnetization rotation layer 50can be made smooth. If the intermediate layer 40 a is made of alaminated film in which the above oxide 100 is laminated, the oxide 100serves as a layer for reflecting spin-polarized electrons. It isexpected that this results in decreasing the reversal current densityfor spin injection induced magnetization reversal.

It is preferable that the thickness of the copper (Cu) layer 90 and theabove oxide 100 be e.g. approximately 0.6 to 10 nm in favor of notinterfering with the magnetization reversal of the magnetic recordinglayer 30 and the precession of the magnetization rotation layer 50 andapplying the alternating magnetic field generated by the precession ofthe magnetization rotation layer 50 to the magnetic recording layer 30.

The intermediate layer 40 b is made of a nonmagnetic material. Thematerial of the intermediate layer 40 b can be any of metal, insulator,and semiconductor serving as a spin conduction layer, and can be eithera low-resistance material or a high-resistance material.

The low-resistance material can be copper (Cu), gold (Au), silver (Ag),or aluminum (Al), or a metal containing at least one element selectedfrom the group consisting of copper (Cu), gold (Au), silver (Ag), andaluminum (Al) or an alloy thereof. The thickness of the intermediatelayer 40 b made of such a low-resistance nonmagnetic material can bee.g. approximately 2 to 60 nm to achieve the effect of magnetizationrotation by angular momentum transfer of electron spin.

The high-resistance material can be an insulator made of an oxide,nitride, or fluoride containing at least one element selected from thegroup consisting of aluminum (Al), titanium (Ti), tantalum (Ta), cobalt(Co), nickel (Ni), silicon (Si), magnesium (Mg), and iron (Fe). Thisinsulator is illustratively alumina (Al₂O_(3-x)), magnesium oxide (MgO),SiO₂, Si—O—N, Ta—O, or Al—Zr—O. Alternatively, the high-resistancematerial can also be a semiconductor having a large energy gap such asGaAlAs.

The intermediate layer 40 b can also be made of a nanocontact MRmaterial in which a magnetic layer is inserted into pinholes provided inan insulator, or a CCP-CPP-MR (magnetoresistive effect) material inwhich Cu is inserted into such pinholes, to achieve the effect ofmagnetization rotation. In the case of the former insulator forproviding the tunnel magnetoresistive effect, it is preferable that thethickness of the intermediate layer 40 b be e.g. approximately 0.2 to 2nm in view of signal reproduction. In the case of the latter nanocontactMR or CCP-CPP-MR, it is preferable that the thickness of theintermediate layer 40 b be in the range of e.g. approximately 0.4 to 40nm.

With regard to the cross-sectional shape of the magnetic recordingdevice according to this embodiment, the dimension in the directiongenerally parallel to the film plane (generally horizontal dimension inthis figure) is the same for all the layers in the magnetic recordingdevice of FIG. 1, but is not limited thereto. The dimension of eachlayer may be different for making interconnection or controlling themagnetization direction. For example, the cross section can be shapedlike a trapezoid in which the dimension in the direction generallyparallel to the film plane (generally horizontal dimension in thisfigure) continuously decreases toward the upper layer. Alternatively,the dimension in the direction generally parallel to the film plane(generally horizontal dimension in this figure) can be discontinuousbetween the layers (for example, a convex cross section). Even in thesecases, there is no problem about the effect of this embodiment. However,it Is preferable that the dimension of the magnetization rotation layer50 in the direction generally parallel to the film plane (generallyhorizontal dimension in this figure) be larger than that of the magneticrecording layer 30 because, in this structure, the radio-frequencymagnetic field can be applied more effectively in the direction of themagnetization hard axis of the magnetic recording layer 30.

The planar shape of the magnetic recording device according to thisembodiment, in the case of the magnetic recording layer 30 with amagnetization easy axis directed generally parallel to the film plane,is preferably a rectangle, a horizontally long (vertically long)hexagon, an ellipse, a rhombus, or a parallelogram having avertical-to-horizontal ratio in the range of e.g. approximately 1:1.2 to1:5, that is, in terms of horizontal/vertical aspect ratio, in the rangeof e.g. approximately 1.2 to 5. In the case of the magnetic recordinglayer 30 with a magnetization easy axis directed generally perpendicularto the film plane, the horizontal/vertical aspect ratio is preferably inthe range of e.g. approximately 1 to 10. With regard to the dimensionsin the planar shape of the magnetic layer, it is preferable that theside along the minor axis be in the range of e.g. approximately 5 to 300nm.

In the following, variations of this embodiment are described withreference to specific examples.

FIG. 5 is a schematic view illustrating the cross-sectional structure ofa magnetic recording device according to a specific example of thisembodiment.

The magnetic recording device of this specific example is different fromthe magnetic recording device of FIG. 1 in that the magnetization 12 aof the magnetic pinned layer 10 a is fixed generally perpendicular tothe film plane, and that the magnetization easy axis 34 of the magneticrecording layer 30 is generally perpendicular to the film plane. Thelamination order of the layers of this specific example is the same asthat of the magnetic recording device of FIG. 1. Like the magneticrecording device of FIG. 1, the intermediate layer 40 a disposed betweenthe magnetic recording section 3 and the magnetization oscillator 5comprises a spin quenching layer, and can be made of the materialdescribed above. An electron current 60 can be passed through themagnetic recording device shown in FIG. 5 using electrodes, not shown,connected to the magnetic pinned layers 10 a, 10 b.

In the magnetic recording device of this specific example, in the casewhere an electron current 60 flows from the magnetic pinned layer 10 ato the magnetic recording layer 30 in FIG. 5 (downward in this figure),electrons passing through the magnetic pinned layer 10 a take on spinparallel to the magnetization 12 a. Hence the magnetic recording layer30 takes on a magnetization 32 parallel (upward in this figure) to themagnetization 12 a.

Simultaneously with this write operation, in the case where the electroncurrent 60 flows from the magnetization rotation layer 50 to themagnetic pinned layer 10 b (downward in this figure), electrons withspin parallel to the magnetization 12 b of the magnetic pinned layer 10b pass through the magnetic pinned layer 10 b, whereas electrons withspin antiparallel to the magnetization 12 b are reflected at theinterface between the magnetic pinned layer 10 b and the intermediatelayer 40 b. When these reflected electrons flow into the magnetizationrotation layer 50, the magnetization of the magnetization rotation layer50 undergoes precession by the effect of the electron spin.Consequently, a radio-frequency magnetic field is generated from themagnetization rotation layer 50.

On the other hand, the electron current 60 that has passed through themagnetic recording layer 30 of the magnetic recording section 3 alsoacts on the magnetization of the magnetization rotation layer 50 of themagnetization oscillator 5. However, the intermediate layer 40 adisposed between the magnetic recording layer 30 and the magnetizationrotation layer 50 is a spin quenching layer, and hence the spininformation of electrons traversing this layer is lost. Thus, themagnetization of the magnetization rotation layer 50 can be controlledindependently of the effect of the spin transfer torque from themagnetic recording layer 30.

In contrast, in the case where an electron current 60 flows from themagnetic recording layer 30 to the magnetic pinned layer 10 a in FIG. 5(upward in this figure), electrons with spin parallel to themagnetization 12 a of the magnetic pinned layer 10 a pass through themagnetic pinned layer 10 a, whereas electrons with spin antiparallel tothe magnetization 12 a are reflected at the interface between themagnetic pinned layer 10 a and the barrier layer 20. When thesereflected electrons flow into the magnetic recording layer 30, themagnetic recording layer 30 takes on a magnetization 32 antiparallel(downward in this figure) to the magnetization 12 a by the effect of theelectron spin.

Simultaneously with this write operation, in the case where the electroncurrent 60 flows from the magnetic pinned layer 10 b to themagnetization rotation layer 50 (upward in this figure), electronspassing through the magnetic pinned layer 10 b take on spin parallel tothe magnetization 12 b. When these electrons flow into the magnetizationrotation layer 50, the magnetization of the magnetization rotation layer50 undergoes precession by the effect of the electron spin.Consequently, a radio-frequency magnetic field is generated from themagnetization rotation layer 50.

On the other hand, part of the electron current 60 that has flowed fromthe magnetization rotation layer 50 of the magnetization oscillator 5 tothe magnetic recording layer 30 of the magnetic recording section 3 isreflected at the surface of the magnetic recording layer 30 and alsoacts on the magnetization of the magnetization rotation layer 50 of themagnetization oscillator 5. However, the intermediate layer 40 adisposed between the magnetic recording layer 30 and the magnetizationrotation layer 50 includes a material or structure such that the spinpolarization of electrons traversing the intermediate layer 40 a isquenched, and hence the spin information is lost. Thus, themagnetization of the magnetization rotation layer 50 can be controlledindependently of the effect of the spin transfer torque from themagnetic recording layer 30.

The frequency of the radio-frequency magnetic field is, like theforegoing, approximately 1 to 60 GHz, for example. This radio-frequencymagnetic field has a component perpendicular to the magnetization easyaxis of the magnetic recording layer 30, that is, in the direction ofits magnetization hard axis. Hence, the radio-frequency magnetic fieldgenerated from the magnetization rotation layer 50 is applied in thedirection of the magnetization hard axis of the magnetic recording layer30. When the radio-frequency magnetic field generated from themagnetization rotation layer 50 is applied in the direction of themagnetization hard axis of the magnetic recording layer 30, themagnetization 32 of the magnetic recording layer 30 becomes very easy tobe reversed.

In the magnetic recording device of this specific example, themagnetization easy axis 34 of the magnetic recording layer 30 isgenerally perpendicular to the film plane. Thus the radio-frequencymagnetic field generated from the magnetization rotation layer 50 isconstantly applied in the direction of the magnetization hard axis ofthe magnetic recording layer 30. Hence the magnetization 32 of themagnetic recording layer 30 can be reversed more efficiently than in themagnetic recording device of FIG. 1.

FIG. 6 is a schematic view illustrating the cross-sectional structure ofa magnetic recording device according to another specific example ofthis embodiment.

The magnetic recording device of this specific example comprises amagnetic recording layer 30 with a magnetization easy axis 34 directedgenerally perpendicular to the film plane, a magnetic pinned layer 10 awith a magnetization 12 a fixed generally perpendicular to the filmplane, a barrier layer 20 disposed between the magnetic recording layer30 and the magnetic pinned layer 10 a, a magnetization rotation layer 50with a magnetization easy axis 54 directed generally parallel to thefilm plane, and an intermediate layer 40 a disposed between the magneticpinned layer 10 a and the magnetization rotation layer 50. In themagnetic recording device of this specific example, the magnetizationrotation layer 50, the intermediate layer 40 a, the magnetic pinnedlayer 10 a, the barrier layer 20, and the magnetic recording layer 30are laminated in this order. In contrast to the magnetic recordingdevice shown in FIGS. 1 and 5, the intermediate layer 40 a of thisspecific example is made of a so-called spin transfer layer, whichincludes a material described later that can transfer spin information.An electron current 60 can be passed through the magnetic recordingdevice shown in FIG. 6 using electrodes, not shown, connected to themagnetic recording layer 30 and the magnetization rotation layer 50.

The magnetic pinned layer 10 a serves to determine the orientation ofthe magnetization 32 of the magnetic recording layer 30, and also servesto cause the magnetization 54 of the magnetization rotation layer 50 toundergo precession. That is, the magnetic pinned layer 10 asimultaneously serves as the magnetic pinned layer of both the magneticrecording section 3 and the magnetization oscillator 5. Such a structuresimplifies the structure of the magnetic recording device. Thus theoverall thickness can be decreased, and the magnetic recording devicecan be downsized. Furthermore, the manufacturing yield is improved.

In the magnetic recording device shown in FIG. 6, the intermediate layer40 a is made of a so-called spin transfer layer, which includes amaterial that can transfer spin information. Preferably, specificmaterials for the intermediate layer 40 a include a metal selected fromthe group consisting of copper (Cu), gold (Au), silver (Ag), andaluminum (Al) or an alloy containing at least one element thereof, or aninsulator made of an oxide, nitride, or fluoride containing at least oneelement selected from the group consisting of aluminum (Al), titanium(Ti), tantalum (Ta), cobalt (Co), nickel (Ni), silicon (Si), magnesium(Mg), and iron (Fe).

In the case of the above nonmagnetic metals, the thickness of theintermediate layer 40 a can be e.g. approximately 2 to 60 nm to achievethe effect of magnetization rotation by the angular momentum of electronspin. Examples of the above insulator also include alumina (Al₂O_(3-x)),magnesium oxide (MgO), SiO₂, Si—O—N, Ta—O, and Al—Zr—O, as well as asemiconductor having a large energy gap such as GaAlAs. In such cases,it is preferable that the thickness of the intermediate layer 40 a be inthe range of e.g. approximately 0.6 to 2 nm to achieve sufficientconductivity.

In the case where an electron current 60 flows from the magneticrecording layer 30 to the magnetic pinned layer 10 a in FIG. 6 (downwardin this figure), electrons with spin parallel to the magnetization 12 aof the magnetic pinned layer 10 a pass through the magnetic pinned layer10 a, whereas electrons with spin antiparallel to the magnetization 12 aare reflected at the interface between the magnetic pinned layer 10 aand the barrier layer 20, When these reflected electrons flow into themagnetic recording layer 30, the magnetic recording layer 30 takes on amagnetization 32 antiparallel (downward in this figure) to themagnetization 12 a by the effect of the electron spin.

Simultaneously with this write operation, the electron current 60 flowsfrom the magnetic pinned layer 10 a to the magnetization rotation layer50 (downward in this figure), and hence electrons passing through themagnetic pinned layer 10 a take on spin parallel to the magnetization 12a. When these electrons flow into the magnetization rotation layer 50,the magnetization of the magnetization rotation layer 50 undergoesprecession by the effect of the electron spin. Consequently, aradio-frequency magnetic field is generated from the magnetizationrotation layer 50.

In contrast, in the case where an electron current 60 flows from themagnetic pinned layer 10 a to the magnetic recording layer 30 in FIG. 6(upward in this figure), electrons passing through the magnetic pinnedlayer 10 a take on spin parallel to the magnetization 12 a. Hence themagnetic recording layer 30 takes on a magnetization 32 parallel (upwardin this figure) to the magnetization 12 a.

Simultaneously with this write operation, the electron current 60 flowsfrom the magnetization rotation layer 50 to the magnetic pinned layer 10a (upward in this figure), and hence electrons with spin parallel to themagnetization 12 a of the magnetic pinned layer 10 a pass through themagnetic pinned layer 10 a, whereas electrons with spin antiparallel tothe magnetization 12 a are reflected at the interface between themagnetic pinned layer 10 a and the intermediate layer 40 a. When thesereflected electrons flow into the magnetization rotation layer 50, themagnetization of the magnetization rotation layer 50 undergoesprecession by the effect of the electron spin. Consequently, aradio-frequency magnetic field is generated from the magnetizationrotation layer 50.

The frequency of the radio-frequency magnetic field is, like theforegoing, approximately 1 to 60 GHz, for example. This radio-frequencymagnetic field has a component perpendicular to the magnetization easyaxis of the magnetic recording layer 30, that is, in the direction ofits magnetization hard axis. Hence, the radio-frequency magnetic fieldgenerated from the magnetization rotation layer 50 is applied in thedirection of the magnetization hard axis of the magnetic recording layer30. When the radio-frequency magnetic field generated from themagnetization rotation layer 50 is applied in the direction of themagnetization hard axis of the magnetic recording layer 30, themagnetization 32 of the magnetic recording layer 30 becomes very easy tobe reversed.

In the magnetic recording device of this specific example, like themagnetic recording device of FIG. 5, the magnetization easy axis 34 ofthe magnetic recording layer 30 is generally perpendicular to the filmplane. Thus the radio-frequency magnetic field generated from themagnetization rotation layer 50 is constantly applied in the directionof the magnetization hard axis of the magnetic recording layer 30. Hencethe magnetization 32 of the magnetic recording layer 30 can be reversedmore efficiently than in the magnetic recording device of FIG. 1.

It is noted that the magnetic recording layer 30 is not limited to beingprovided with a single magnetic pinned layer as in the magneticrecording device shown in FIG. 6. In a structure (dual pin structure)where another magnetic pinned layer is formed on the magnetic recordinglayer 30 shown in FIG. 6 via another intermediate layer, the criticalreversal current for spin injection induced magnetization reversal canbe decreased.

FIG. 7 is a schematic view illustrating the cross-sectional structure ofa magnetic recording device according to still another specific exampleof this embodiment.

In the magnetic recording device of this specific example, thelamination order in the magnetic recording section 3 is different fromthat in the magnetic recording device of FIG. 1. In the magneticrecording section 3 of the magnetic recording device of this specificexample, the magnetic pinned layer 10 a, the barrier layer 20, and themagnetic recording layer 30 are laminated in this order. In contrast, inthe magnetic recording section 3 of the magnetic recording device ofFIG. 1, the magnetic recording layer 30, the barrier layer 20, and themagnetic pinned layer 10 a are laminated in this order. Between themagnetic pinned layer 10 a and the intermediate layer 40 a, anantiferromagnetic layer, not shown, can be disposed to reinforce themagnetization pinning of the magnetic pinned layer 10 a. An electroncurrent 60 can be passed through the magnetic recording device of thisspecific example using electrodes, not shown, connected to the magneticrecording layer 30 and the magnetic pinned layer 10 b. In thisstructure, the intermediate layer 40 a can be optionally either a spinquenching layer or a spin transfer layer.

In the magnetic recording device of this specific example, in the casewhere an electron current 60 flows from the magnetic recording layer 30to the magnetic pinned layer 10 a in FIG. 7 (downward in this figure),electrons with spin parallel to the magnetization 12 a of the magneticpinned layer 10 a pass through the magnetic pinned layer 10 a, whereaselectrons with spin antiparallel to the magnetization 12 a are reflectedat the interface between the magnetic pinned layer 10 a and the barrierlayer 20. When these reflected electrons flow into the magneticrecording layer 30, the magnetic recording layer 30 takes on amagnetization 32 antiparallel (rightward in this figure) to themagnetization 12 a by the effect of the electron spin.

Simultaneously with this write operation, in the case where the electroncurrent 60 flows from the magnetization rotation layer 50 to themagnetic pinned layer 10 b (downward in this figure), electrons withspin parallel to the magnetization 12 b of the magnetic pinned layer 10b pass through the magnetic pinned layer 10 b, whereas electrons withspin antiparallel to the magnetization 12 b are reflected at theinterface between the magnetic pinned layer 10 b and the intermediatelayer 40 b. When these reflected electrons flow into the magnetizationrotation layer 50, the magnetization of the magnetization rotation layer50 undergoes precession by the effect of the electron spin.Consequently, a radio-frequency magnetic field is generated from themagnetization rotation layer 50.

In contrast, in the case where an electron current 60 flows from themagnetic pinned layer 10 a to the magnetic recording layer 30 in FIG. 7(upward in this figure), electrons passing through the magnetic pinnedlayer 10 a take on spin parallel to the magnetization 12 a. Hence themagnetic recording layer 30 takes on a magnetization 32 parallel(leftward in this figure) to the magnetization 12 a.

Simultaneously with this write operation, in the case where the electroncurrent 60 flows from the magnetic pinned layer 10 b to themagnetization rotation layer 50 (upward in this figure), electronspassing through the magnetic pinned layer 10 b take on spin parallel tothe magnetization 12 b. When these electrons flow into the magnetizationrotation layer 50, the magnetization of the magnetization rotation layer50 undergoes precession by the effect of the electron spin.Consequently, a radio-frequency magnetic field is generated from themagnetization rotation layer 50.

The frequency of the radio-frequency magnetic field is, like theforegoing, approximately 1 to 50 GHz, for example. This radio-frequencymagnetic field has a component perpendicular to the magnetization easyaxis of the magnetic recording layer 30, that is, in the direction ofits magnetization hard axis. Hence, the radio-frequency magnetic fieldgenerated from the magnetization rotation layer 50 is applied in thedirection of the magnetization hard axis of the magnetic recording layer30. When the radio-frequency magnetic field generated from themagnetization rotation layer 50 is applied in the direction of themagnetization hard axis of the magnetic recording layer 3 n, themagnetization 32 of the magnetic recording layer 30 becomes very easy tobe reversed.

In the magnetic recording device of this specific example, the magneticrecording layer 30 is located more distant from the magnetizationrotation layer 50 than in the magnetic recording device of FIG. 1.However, also in the magnetic recording device of this specific example,the radio-frequency magnetic field generated from the magnetizationrotation layer 50 is applied in the direction of the magnetization hardaxis of the magnetic recording layer 30, and advantageously, themagnetization 32 of the magnetic recording layer 30 becomes very easy tobe reversed.

Next, a description is given of a simulation of the magnetizationreversal of the magnetic recording layer performed on the magneticrecording device of this embodiment.

FIG. 8 is a graph illustrating the temporal variation of magnetizationreversal in the case where writing is performed without applying aradio-frequency magnetic field to the magnetic recording layer.

FIG. 9 is a graph illustrating the temporal variation of magnetizationreversal in the case where writing is performed while applying aradio-frequency magnetic field to the magnetic recording layer.

FIG. 10 is a graph illustrating the temporal variation of magneticreversal in the case where writing is performed while applying aradio-frequency magnetic field having different frequencies to themagnetic recording layer. More specifically, FIG. 10A shows the casewhere the frequency is 0.1 GHz, FIG. 10B shows the case where thefrequency is 2 GHz, FIG. 10C shows the case where the frequency is 4GHz, FIG. 10D shows the case where the frequency is 10 GHz, and FIG. 10Eshows the case where the frequency is 15 GHz.

The horizontal axis in FIGS. 8 to 10 represents time required frompassing a write current until magnetization reversal. The vertical axisin FIGS. 8 to 10 represents the orientation of the magnetization of themagnetic recording layer. That is, the graph indicates thatmagnetization reversal occurs when the value on the vertical axis variesfrom 1.0 to −1.0.

This simulation is based on the Landau-Lifshitz-Gilbert equationincluding spin transfer torque given by the following equation, where Mdenotes the vector of the magnetization 32 of the magnetic recordinglayer 30, and m and m_(pin) denote the unit vector along themagnetization 32 of the magnetic recording layer 30 and themagnetization 12 a of the magnetic pinned layer 10 a, respectively.H_(eff) is the effective magnetic field applied to the magneticrecording layer 30, to which the effect of the radio-frequency magneticfield was added.dM/d=−γM×H _(eff) +am×(dM/dt)+(2μ_(B) /V)(I/e)gm×(m _(pin) ×m)

The basic structure of the magnetic recording section 3 in thissimulation is: magnetic recording layer 30/barrier layer 20/magneticpinned layer 10 a. The magnetic recording layer 30 is made of cobalt(Co) and has a thickness of 2.5 nm. The magnetic pinned layer 10 a ismade of cobalt (Co) and has a thickness of 40 nm. The magnetic recordinglayer 30 has an elliptical shape of approximately 120 nm×90 nm. Themagnetization easy axis of the magnetic recording layer 30 is directedgenerally parallel to the film plane, and in particular, generally inthe direction of the ellipse major axis. The anisotropy magnetic fieldwas assumed to have a typical value of 150 Oe (oersted). Theseparameters were selected on the basis of the result of preliminaryexperiments.

The critical reversal current density (Jc) for this magnetic recordingdevice is calculated to be 2×10⁷ A/cm². However, this critical reversalcurrent density (Jc) is a current value needed in the case where aquasi-static current is passed. If the pulse width decreases, a reversalcurrent density more than several times the critical reversal currentdensity (Jc) is needed as described above.

In the simulation shown in FIG. 8, magnetization reversal (writing) wasperformed by a current of 2.86 times the critical reversal currentdensity (Jc) without applying a radio-frequency magnetic field to themagnetic recording layer 30. FIG. 8 includes a plurality of curves,because the results for different initial angles of the magnetization 32of the magnetic recording layer 30 are superimposed. The initial angleof the magnetization 32 of the magnetic recording layer 30 wasdistributed to a maximum of 0.57 degrees with respect to themagnetization easy axis. It can be seen that, although a current of 2.86times the critical reversal current density (Jc) is passed perpendicularto the magnetic recording device, the reversal time is varied with theinitial angle of the magnetization 32 of the magnetic recording layer30. Hence, in the case where the write current has a pulse width ofapproximately 5 ns, the reversal probability is approximately ½. Thissimulation result shows that, for a pulse width of e.g. approximately 5ns, a larger write current is needed to achieve a reversal probabilityof 1 without applying a radio-frequency magnetic field to the magneticrecording layer 30.

In the simulation shown in FIG. 9, magnetization reversal (writing) wasperformed by a current of 2.86 times the critical reversal currentdensity (Jc) like the simulation shown in FIG. 8, while applying aradio-frequency magnetic field having an amplitude of 3 Oe and afrequency of 4.75 GHz to the magnetic recording layer 30 in thedirection of its magnetization hard axis. Like the simulation shown inFIG. 8, the initial angle of the magnetization 32 of the magneticrecording layer 30 was distributed to a maximum of 0.57 degrees withrespect to the magnetization easy axis. Also in this figure, the resultsfor different initial angles are superimposed. It can be seen that, incontrast to the simulation result shown in FIG. 8, as a consequence ofapplying a radio-frequency magnetic field to the magnetic recordinglayer 30, the magnetization is reversed in a time period ofapproximately 1.3 ns irrespective of the initial angle of themagnetization 32 of the magnetic recording layer 30. This indicates thatrapid magnetization reversal with low variation can be achieved,allowing substantial reduction of recording current density.

In the simulation shown in FIG. 10, magnetization reversal (writing) wasperformed by a current of 2.86 times the critical reversal currentdensity (Jc) like the simulation shown in FIG. 8, while applying aradio-frequency magnetic field having an amplitude of 7.5 Oe to themagnetic recording layer 30 in the direction of its magnetization hardaxis. It can be seen from this simulation result that the reversal timeis varied with the initial angle of the magnetization 32 of the magneticrecording layer 30 in any of the cases where the frequency of theradio-frequency magnetic field is 0.1 GHz, 2 GHz, 10 GHz, and 15 GHz. Incontrast, in the case where the frequency of the radio-frequencymagnetic field is 4 GHz, it can be seen that the magnetization isreversed in a time period of approximately 0.9 ns irrespective of theinitial angle of the magnetization 32 of the magnetic recording layer30. That is, it turns out that a frequency of e.g. approximately 4 GHz,at which the magnetic recording layer 30 undergoes magnetic resonance,is preferable as a condition for realizing rapid magnetization reversalwith low variation. It is noted that the frequency of magnetic resonancein a magnetic recording device can be determined by connecting themagnetic recording device to a network analyzer to characterize theresponse (transmittance or reflectance) of the magnetic recording deviceto radio frequencies.

FIG. 11 is a schematic illustration of the dependence of time requiredfor magnetization reversal on frequency and radio-frequency magneticfield intensity in the case where writing is performed on the magneticrecording layer 30 with a magnetization easy axis directed generallyperpendicular to the film plane while applying a radio-frequencymagnetic field to the magnetic recording layer.

As the characteristics of the magnetic recording device, a perpendicularmagnetic anisotropy (Ku) of 6.2×10⁶ erg/cc and a magnetization (Ms) of970 emu/cc were assumed. In this case, the anisotropy magnetic field(Hk) is 12.8 kOe, and the critical reversal current density (Jc) for DCcurrent is 1.69×10⁶ A/cm².

Like the simulations shown in FIGS. 8 to 10, the basic structure of themagnetic recording section 3 in this simulation is: magnetic recordinglayer 30/barrier layer 20/magnetic pinned layer 10 a. Specifically, thestructure FeXY/MgO/FeXY is assumed. X is at least one element selectedfrom the group consisting of chromium (Cr), copper (Cu), cobalt (Co),nickel (Ni), and vanadium (V). Y is platinum (Pt) or palladium (Pd). Itis noted that TMR (tunneling magnetoresistive effect) can be increasedby interposing an interfacial layer made of FeX at the interface betweenFeXY and MgO.

A radio-frequency magnetic field at 1 to 7 GHz was applied to thismagnetic recording device in the direction parallel to the film plane,that is, in the direction of the magnetization hard axis, to examine thebehavior of magnetization reversal. The intensity of the radio-frequencymagnetic field was varied as 26 Oe, 64 Oe, and 128 Oe. With regard tocurrent, magnetization reversal (writing) was performed by a current of1.64 times the critical reversal current density (Jc). Like thesimulations shown in FIGS. 8 to 10, the reversal time is varied with theinitial angle of the magnetization 32 of the magnetic recording layer30. Among them, the longest reversal time is plotted with respect to thefrequency of the radio-frequency magnetic field in FIG. 11.

In the vicinity of the zero frequency of the radio-frequency magneticfield, FIG. 11 shows reversal time for no radio-frequency magnetic fieldapplied. It can be seen from this that the time required for reversalreaches approximately 20 ns in the case where no radio-frequencymagnetic field is applied. It turns out from this result that, in thecase where magnetization reversal (writing) is performed using a currentpulse illustratively having a pulse width of approximately 8 ns and acurrent density of 2.77×10⁶ A/cm², no magnetization reversal actuallyoccurs without application of a radio-frequency magnetic field, whereasapplication of a radio-frequency magnetic field illustratively having afrequency of approximately 2.2 GHz and an intensity of approximately 0.2to 1% of the anisotropy magnetic field (Hk) enables magnetizationreversal with a reversal probability of 1. Furthermore, it turns outthat the frequency out of the resonant condition is unfavorable even ifthe radio-frequency magnetic field has high intensity.

As described above, irrespective of whether the magnetization easy axis34 of the magnetic recording layer 30 is parallel or perpendicular tothe film plane, a radio-frequency magnetic field having a frequencysimilar to the magnetic resonance frequency of the magnetic recordinglayer 30 is applied in the direction of the magnetization hard axis ofthe magnetic recording layer 30, and thereby rapid magnetizationreversal with low variation can be achieved, allowing substantialreduction of recording current density.

Next, this embodiment is described in more detail with reference to aworking example.

FIG. 12 is a table showing the result of writing probability in thisworking example.

In this working example, a magnetic recording device having a structuresimilar to FIG. 1 was prototyped (sample number 51). The material andthickness of the layers of this magnetic recording device are asfollows: antiferromagnetic layer (IrMn)/magnetic pinned layer 10 a(CoFeB: 4 nm/Ru: 1 nm/CoFe: 4 nm)/barrier layer 20 (MgO: 1 nm)/magneticrecording layer 30 (CoFe: 1 nm/CoFeB: 1 nm)/intermediate layer 40 a (Ru:6 nm)/magnetization rotation layer 50 (CoFe: 2 nm)/intermediate layer 40b (Cu: 6 nm)/magnetic pinned layer 10 b (FePt: 10 nm). Furthermore,magnetic recording devices having layer structures R1 to R3 wereprototyped as comparative examples. Thus, four samples were prepared intotal. In the case of the magnetization 12 b of the magnetic pinnedlayer 10 b and/or the magnetization easy axis of the magnetizationrotation layer 50 being generally perpendicular to the film plane, themagnetic pinned layer 10 b was made of an FePt ordered alloy in common.

These samples are manufactured by the following procedure.

First, a lower electrode is formed on a wafer, which is then placed inan ultrahigh vacuum sputtering system. Next, a magnetic pinned layer 10b, an intermediate layer 40 b, a magnetization rotation layer 50, anintermediate layer 40 a, a magnetic recording layer 30, a barrier layer20, a magnetic pinned layer 10 a, and a cap layer, not shown, arelaminated in this order on the lower electrode. The lower electrode canbe illustratively made of an Au(001) or Pt(001) buffer layer.

The magnetic pinned layer 10 b made of an FePt ordered alloy can begrown on the buffer layer, not shown, under substrate heating, forexample. Then the substrate temperature is decreased to roomtemperature, and the intermediate layer 40 b and the subsequent layersare formed. Then the cap layer, not shown, is grown. However, formationof the barrier layer 20 was followed by post-annealing at 300° C. Thissubstrate was placed in an in-field heat treatment furnace and subjectedto heat treatment in a magnetic field at 270° C. for two hours toprovide the antiferromagnetic layer with exchange bias capability.

Next, an EB (electron beam) resist is applied and subjected to EBexposure to form a mask. The mask is illustratively shaped like anellipse of 70 nm×140 nm, and the longitudinal direction along its majoraxis is parallel to the direction of the magnetic anisotropy of themagnetic recording layer 30. Then an ion milling system is used to etchthe magnetic recording layer 30, the magnetic pinned layers 10 a, 10 b,the nonmagnetic barrier layer 20, and the cap layer, not shown, locatedin the region not covered with the mask. Here, the etching amount can beaccurately ascertained by introducing the sputtered particles into adifferentially pumped quadrupole analyzer for mass spectrometry.

Subsequently, the mask is removed, and SiO₂ is formed to completelycover the magnetic recording device. Then the SiO₂ surface is planarizedby ion milling to expose the upper surface of the cap layer, not shown,from SiO₂. Finally, an upper electrode is formed on the cap layer, notshown.

Using a current having a pulse width of 2 nsec, a write test wasperformed fifty times on the samples thus fabricated. FIG. 12 shows theresult for writing probability in this test. The reversal probabilitywas 1 for the sample S1, but 0.1 for the sample R1, exhibiting reversalvariation. No reversal occurred in the samples R2, R3. It is clearlyconfirmed from this result that, according to this embodiment, variationin magnetization reversal is eliminated, allowing rapid magnetizationreversal and reduction of magnetization reversal current. Furthermore, asimilar trend was observed also for the nonmagnetic barrier layer madeof Al₂O_(3-x), SiO_(2-x), TiO_(x), and ZnO_(x).

Next, a second embodiment of the invention is described.

FIG. 13 is a schematic view illustrating a basic cross-sectionalstructure of a magnetic recording device according to the secondembodiment of the invention.

FIG. 14 is a schematic view illustrating another basic cross-sectionalstructure of a magnetic recording device according to the secondembodiment of the invention.

The magnetic recording device of this embodiment comprises a magneticrecording section 3, an intermediate layer 40 a, and a magnetizationrotation layer 50. In the magnetic recording device of FIG. 13, themagnetic recording section 3 includes a magnetic pinned layer 10 a witha magnetization 12 a fixed generally perpendicular to the film plane, amagnetic recording layer 30 with a magnetization easy axis 34 directedgenerally perpendicular to the film plane, and a barrier layer 20disposed between the magnetic pinned layer 10 a and the magneticrecording layer 30. In the magnetic recording device of FIG. 14, themagnetic recording section 3 includes a magnetic pinned layer 10 a witha magnetization 12 a fixed generally parallel to the film plane, amagnetic recording layer 30 with a magnetization easy axis 34 directedgenerally parallel to the film plane, and a barrier layer 20 disposedbetween the magnetic pinned layer 10 a and the magnetic recording layer30. As in the first embodiment, this laminated structure composed of themagnetic pinned layer 10 a, the barrier layer 20, and the magneticrecording layer 30 is known as MTJ (magnetic tunnel junction).

In the magnetic recording device of this embodiment, the magnetizationof the magnetization rotation layer 50 is oscillated by a thermallyexcited spin wave without using the spin transfer torque from themagnetic pinned layer as in the magnetic recording device describedabove with reference to FIGS. 1, 5, 6, and 7. Generating a thermallyexcited spin wave in a fine magnetic material enables the magnetizationto oscillate at the resonant frequency. Consequently, a radio-frequencymagnetic field can be generated outside the magnetic material. Let Kudenote the magnetic anisotropy of the fine magnetic material, V thevolume, k the Boltzmann constant, and T the temperature. Then KuV/kT ispreferably less than 3 for thermal excitation. At this value or higher,thermally induced oscillation is difficult to occur. Furthermore, Ku ispreferably 400 J/m³ or more. At a value less than this, the frequency ofthe radio-frequency magnetic field is less than GHz, which is less thanthe resonant frequency of the magnetic recording layer 30 and does notsatisfy the characteristics required for an oscillator. Thus it ispreferable that the following formula be satisfied as a condition forthe magnetic anisotropy of the magnetization rotation layer 50 in thisembodiment:400(J/m³)<Ku<3kT/VIt can be seen that this is significantly different from the conditionfor the magnetic recording layer described earlier.

To perform recording on this magnetic recording device, at least, acurrent needs to be passed between the magnetic pinned layer 10 a andthe magnetic recording layer 30. If an electron current is passed usingelectrodes, not shown, connected to the magnetic pinned layer 10 a andthe magnetization rotation layer 50, the intermediate layer 40 a and themagnetization rotation layer 50 are located on the current path. In thiscase, the intermediate layer 40 a is made of a spin quenching layer. Ifspin information is retained in the intermediate layer 40 a, themagnetization rotation layer 50 responds to the effect of the spininformation (spin transfer torque) of spin-polarized electrons passingthrough or reflected at the magnetic recording layer 30, and themagnetization of the magnetization rotation layer 50 is interlocked withthe magnetic recording layer 30, hence failing to operate as anoscillator. To prevent this, the spin quenching layer is needed.

The magnetization rotation layer 50 can be made of a normal ferromagnet.In the case of using cobalt (Co) or a cobalt (Co) alloy, themagnetization easy axis of the magnetization rotation layer 50 isgenerally perpendicular to the film plane. In the case where themagnetization rotation layer with a magnetization easy axis directedgenerally perpendicular to the film plane is fluctuated, aradio-frequency magnetic field having a component generally parallel tothe film plane can be produced. Hence the effect of as radio-frequencymagnetic field produced by the magnetization rotation layer 50 can beequally achieved irrespective of whether the magnetization easy axis ofthe magnetic recording layer 30 is perpendicular or parallel to the filmplane as shown in FIGS. 13 and 14.

Thus, in the magnetic recording device of this embodiment, the leakagemagnetic field from the magnetization rotation layer 50 can be appliedas a radio-frequency magnetic field to the magnetic recording layer 30by using the basic structure: magnetic pinned layer 10 a/barrier layer20/magnetic recording layer 30/intermediate layer 40 a/magnetizationrotation layer 50.

In the magnetic recording device of this embodiment, anantiferromagnetic layer, not shown, can be attached to the magneticpinned layer 10 a to reinforce the pinning effect thereof. Furthermore,the effect of this embodiment is the same even if the magnetic recordingdevice is inverted upside down in these figures. Moreover, in thestructure with the magnetic recording device inverted upside down, theend point of multilayer milling can be located immediately above themagnetic pinned layer 10 a, or halfway through the magnetic pinned layer10 a. The effect of this embodiment is the same even if the end point islocated immediately above or halfway through the intermediate layer 40a.

In the following, this embodiment is described in more detail withreference to specific examples.

FIG. 15 is a schematic view illustrating the cross-sectional structureof a magnetic recording device according to a specific example of thisembodiment.

FIG. 16 is a schematic view illustrating the cross-sectional structureof a magnetic recording device according to another specific example ofthis embodiment.

The magnetic recording device shown in FIGS. 15 and 16 comprises amagnetic recording section 3, an intermediate layer 40 a, amagnetization rotation layer 50, and a buffer layer 70. In the magneticrecording device shown in FIG. 15, the magnetic recording section 3includes a magnetic pinned layer 10 a with a magnetization 12 a fixedgenerally perpendicular to the film plane, a magnetic recording layer 30with a magnetization easy axis 34 directed generally perpendicular tothe film plane, and a barrier layer 20 disposed between the magneticpinned layer 10 a and the magnetic recording layer 30. In the magneticrecording device shown in FIG. 16, the magnetic recording section 3includes a magnetic pinned layer 10 a with a magnetization 12 a fixedgenerally parallel to the film plane, a magnetic recording layer 30 witha magnetization easy axis 34 directed generally parallel to the filmplane, and a barrier layer 20 disposed between the magnetic pinned layer10 a and the magnetic recording layer 30.

In the magnetic recording device of both these specific examples, thebuffer layer 70, the magnetization rotation layer 50, the intermediatelayer 40 a, the magnetic recording layer 30, the barrier layer 20, andthe magnetic pinned layer 10 a are laminated in this order. These layersare made of materials as follows: magnetic pinned layer 10 a, CoFePt;barrier layer 20, MgO; magnetic recording layer 30, CoFePt; intermediatelayer 40 a, ruthenium (Ru); magnetization rotation layer 50, cobalt(Co); buffer layer 70, ruthenium (Ru). An electron current 60 can bepassed through this magnetic recording device using electrodes, notshown, connected to the magnetic pinned layer 10 a and the buffer layer70.

In the magnetic recording device of these specific examples, the bufferlayer 70 made of ruthenium (Ru) is disposed also on the opposite side(lower side in these figures) of the intermediate layer 40 a across themagnetization rotation layer 50. Thus the closest-packed plane of thecobalt (Co) crystal grows parallel to the interface. Consequently, theperpendicular magnetic anisotropy can be strengthened, and the rotationaxis of precession can be clearly defined. This provides the advantageof being able to reduce variation in characteristics. The thickness ofthe magnetization rotation layer 50 made of cobalt (Co) is preferably 10nm or less in view of oscillation characteristics.

FIGS. 17 and 18 are schematic views illustrating the cross-sectionalstructure of magnetic recording devices according to still anotherspecific example of this embodiment.

The magnetic recording device shown in FIGS. 17 and 18 comprises amagnetic recording section 3, intermediate layers 40 a 1, 40 a 2, andmagnetization rotation layers 501, 502. The magnetic recording section 3includes a magnetic pinned layer 10 a with a magnetization 12 a fixedgenerally perpendicular to the film plane, a magnetic recording layer 30with a magnetization easy axis 34 directed generally perpendicular tothe film plane, and a barrier layer 20 disposed between the magneticpinned layer 10 a and the magnetic recording layer 30.

In the magnetic recording device shown in FIG. 17, the magneticrecording layer 30, the barrier layer 20, and the magnetic pinned layer10 a are laminated in this order. The magnetization rotation layers 501,502 are further laminated on the upper surface of the magnetic pinnedlayer 10 a via the intermediate layers 40 a 1, 40 a 2. The magnetizationrotation layers 501, 502 and the intermediate layers 40 a 1, 40 a 2 arenot located on the current path of the magnetic recording section 3, andare insulated from the electron current 60, or have a structure throughwhich no current can flow. Because the intermediate layers 40 a 1, 40 a2 are not located on the current path, the material of the intermediatelayers 40 a 1, 40 a 2 is not limited to that of the spin quenchinglayer, but they can be made of the material of the spin transfer layer,or an insulator.

In the magnetic recording device shown in FIG. 18, the magneticrecording layer 30, the barrier layer 20, and the magnetic pinned layer10 a are laminated in this order. The magnetization rotation layer 501is further laminated on the right side surface of the magnetic pinnedlayer 10 a via the intermediate layer 40 a 1, and the magnetizationrotation layer 502 is further laminated on the left side surface of themagnetic pinned layer 10 a via the intermediate layer 40 a 2. Like themagnetic recording device of FIG. 17, the magnetization rotation layers501, 502 are insulated from the electron current 60, or have a structurethrough which no current can flow. Because the intermediate layers 40 a1, 40 a 2 are not located on the current path, the material of theintermediate layers 40 a 1, 40 a 2 is not limited to that of the spinquenching layer, but they can be made of the material of the spintransfer layer, or an insulator.

Thus, also in the structure where the magnetization rotation layers 501,502 are insulated from the electron current 60, a spin wave is thermallyexcited in the magnetization rotation layers 501, 502 of these specificexamples to generate a radio-frequency magnetic field, achieving thesame effect as described above with reference to FIGS. 13 to 16. It isnoted that, alternatively, the magnetization 12 a and the magnetizationeasy axis 34 can be generally parallel to the film plane.

As described above, according to this embodiment, a spin wave isthermally excited in the magnetization rotation layer 50, 501, 502 togenerate a radio-frequency magnetic field. This improves the reversalefficiency of the magnetization 32 of the magnetic recording layer 30irrespective of whether the magnetization rotation layer 50, 501, 502 islocated on the current path of the magnetic recording section 3. Thisallows reduced variation in magnetization reversal without degradingthermal fluctuation resistance and MR (magnetoresistive effect)characteristics. Moreover, the rate of magnetization reversal can beincreased. Furthermore, the value of write current can be also reduced.

Next, a third embodiment of the invention is described.

FIG. 19 is a plan view illustrating a magnetic recording apparatusaccording to the third embodiment of the invention.

The magnetic recording apparatus of this embodiment uses the magneticrecording device of the first embodiment or the magnetic recordingdevice of the second embodiment as a magnetic cell. A switching device(e.g., transistor) is connected in series to the magnetic cell. Eachmagnetic cell is connected to one addressing row (bit line), and eachswitching device is connected to one addressing column (word line). Themagnetic recording apparatus of this embodiment also includes a powersupply for generating a current having a pulse width of 18 nanosecondsor less and 50 picoseconds or more at the time of recording.

Selection of a magnetic cell is enabled by specifying the word line andthe bit line connected to the magnetic cell. More specifically, the bitline is specified to turn on the switching device, thereby passing acurrent through the magnetic cell interposed between the word line andthe electrode. Here, recording can be performed by passing a writecurrent higher than the critical magnetization reversal current, whichis determined by the size, structure, and composition of the magneticcell. It is noted that, alternatively, the switching device can be madeof a diode. This switching device preferably has a low resistance duringON time.

Because the magnetic recording apparatus of this embodiment uses themagnetic recording device of the first embodiment or the magneticrecording device of the second embodiment as a magnetic cell, it cansignificantly reduce variation in magnetization reversal in the casewhere the recording current has a width of 18 ns or less, particularly10 ns or less. Furthermore, the value of write current can be alsoreduced. It turns out from the simulation result shown in FIG. 11 thatthere is no effect of radio-frequency magnetic field in the case wherethe pulse width is larger than 18 to 20 nanoseconds. A pulse width ofthis value or less is preferable to achieve the effect of reducingvariation. In particular, a write pulse width of 10 nanoseconds or lessis more preferable to significantly achieve the effect. On the otherhand, with a pulse width of less than 50 picoseconds, the time requiredfor reversal cannot be gained.

The embodiments of the invention have been described. However, theinvention is not limited to the foregoing description. The aboveembodiments can be suitably modified by those skilled in the art withoutdeparting from the spirit of the invention, and any such modificationsare also encompassed within the scope of the invention. For example, themagnetic pinned layer of the magnetic recording section can be anantiferromagnetic layer, a synthetic antiferromagnetic layer, or a dualpin structure. Furthermore, the figures related to the magneticrecording device according to the embodiments of the invention can beinverted upside down. Cross sections of the elements may be rectangularas shown in the figures, or may be trapezoidal or any otherconfiguration, including stacked structures where widths of each layersmay be different each other.

The elements included in the above embodiments can be combined with eachother as long as technically feasible without departing from the spiritof the invention, and such combinations are also encompassed within thescope of the invention.

We claim:
 1. A magnetic recording device comprising: a magneticrecording section and a magnetization oscillator; and a firstnonmagnetic layer disposed between the magnetic recording section andthe magnetization oscillator, the magnetic recording section including:a first ferromagnetic layer with a magnetization substantially fixed ina first direction; a second ferromagnetic layer with a variablemagnetization direction; and a second nonmagnetic layer disposed betweenthe first ferromagnetic layer and the second ferromagnetic layer, themagnetization oscillator including a third ferromagnetic layer with avariable magnetization direction; a fourth ferromagnetic layer with amagnetization substantially fixed in a second direction; and a thirdnonmagnetic layer disposed between the third ferromagnetic layer and thefourth ferromagnetic layer, at least one of the first and seconddirection being generally perpendicular to the film plane of the layersof the magnetic recording section and the magnetization oscillator, andthe magnetization direction of the second ferromagnetic layer beinggenerally parallel or antiparallel to the first direction and beingdeterminable in response to the orientation of a current, by passing thecurrent in a direction generally perpendicular to the film plane, andthe magnetization of the third ferromagnetic layer being able to undergoprecession by passing the current.
 2. The device according to claim 1,wherein the first nonmagnetic layer is disposed between the firstferromagnetic layer and the third ferromagnetic layer, spin-polarizedelectrons being able to pass the first nonmagnetic layer.
 3. The deviceaccording to claim 1, wherein the first nonmagnetic layer is disposedbetween the fourth ferromagnetic layer and the third ferromagneticlayer, spin-polarized electrons being able to pass the first nonmagneticlayer.
 4. A magnetic recording device comprising: a magnetic recordingsection in which a first ferromagnetic layer with a magnetizationsubstantially fixed in a first direction, a second ferromagnetic layerwith a variable magnetization direction, and a first nonmagnetic layerdisposed between the first ferromagnetic layer and the secondferromagnetic layer are laminated; and a magnetization oscillatorincluding a third ferromagnetic layer with a variable magnetization, afourth ferromagnetic layer with a magnetization substantially fixed in asecond direction, and a third nonmagnetic layer disposed between thethird ferromagnetic layer and the fourth ferromagnetic layer, and thedevice further comprising: a second nonmagnetic layer disposed betweenthe magnetic recording section and the magnetization oscillator, spinpolarization of electrons being quenched by the second nonmagneticlayer, at least one of the first and second direction being generallyperpendicular to the film plane of the layers of the magnetic recordingsection and the magnetization oscillator, the magnetization direction ofthe second ferromagnetic layer being determinable in response to theorientation of a current, by passing the current in a directiongenerally perpendicular to the film plane, and the magnetization of thethird ferromagnetic layer being able to undergo precession by passingthe current.
 5. The device according to claim 4, wherein the thirdferromagnetic layer, the second nonmagnetic layer, and the secondferromagnetic layer are laminated in this order.
 6. The device accordingto claim 4, wherein the second nonmagnetic layer is made of a metalselected from the group consisting of ruthenium (Ru), tantalum (Ta),tungsten (W), platinum (Pt), palladium (Pd), molybdenum (Mo), niobium(Nb), zirconium (Zr), titanium (Ti), and vanadium (V), or an alloycontaining at least one element thereof, and the second nonmagneticlayer has a thickness of 1.4 nm or more and 20 nm or less.
 7. The deviceaccording to claim 4, wherein the second nonmagnetic layer is: a singlelayer body made of a metal selected from the group consisting ofruthenium (Ru), tantalum (Ta), tungsten (W), platinum (Pt), palladium(Pd), molybdenum (Mo), niobium (Nb), zirconium (Zr), titanium (Ti), andvanadium (V), or an alloy containing at least one element thereof, or alaminated body in which copper (Cu) is laminated on one side or bothsides of the single layer body, or a laminated body in which an oxidecontaining at least one element selected from the group consisting ofaluminum (Al), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co),nickel (Ni), vanadium (V), chromium (Cr), tantalum (Ta), tungsten (W),and ruthenium (Ru) is laminated to one side or both sides of the singlelayer body.
 8. The device according to claim 1, wherein the firstdirection is generally parallel to the film plane of the firstferromagnetic layer, and the second direction is generally perpendicularto the film plane of the fourth ferromagnetic layer.
 9. The deviceaccording to claim 1, wherein the first direction is generallyperpendicular to the film plane of the first ferromagnetic layer, andthe second direction is generally perpendicular to the film plane of thefourth ferromagnetic layer.
 10. The device according to claim 1, whereinthe second nonmagnetic layer includes an electrically insulativematerial, and the current being able to tunnel the second nonmagneticlayer.
 11. A magnetic recording device comprising: a laminated bodyincluding a first ferromagnetic layer with a magnetizationsusbstantially fixed in a first direction, a second ferromagnetic layerwith a variable magnetization direction, and a first nonmagnetic layerdisposed between the first ferromagnetic layer and the secondferromagnetic layer; and a third ferromagnetic layer with a variablemagnetization direction disposed close to the second ferromagneticlayer, the magnetization of the third ferromagnetic layer being able toundergo precession by thermal excitation, the magnetization direction ofthe second ferromagnetic layer being determinable in response to theorientation of a current, by passing the current in a directiongenerally perpendicular to the film plane of the layers of the laminatedbody, and the path of the current not including the third ferromagneticlayer.
 12. The device according to claim 11, wherein the firstnonmagnetic layer includes an electrically insulative material, and thecurrent being able to tunnel the first nonmagnetic layer.
 13. The deviceaccording to claim 4, wherein the first direction is generally parallelto the film plane of the first ferromagnetic layer, and the seconddirection is generally perpendicular to the film plane of the fourthferromagnetic layer.
 14. The device according to claim 4, wherein thefirst direction is generally perpendicular to the film plane of thefirst ferromagnetic layer, and the second direction is generallyperpendicular to the film plane of the fourth ferromagnetic layer. 15.The device according to claim 4, wherein the first nonmagnetic layerincludes an electrically insulative material, and the current being ableto tunnel the first nonmagnetic layer.